The present invention relates to an image forming apparatus capable of high accuracy positioning of a process unit representing image forming section equipped with a LED print head.
In color image forming apparatus, the process unit of each color is configured with a photoconductive drum and members arranged at its peripheral such as a charging device, exposing device, developing device and cleaning device, and a degree of parallelization between each member and the photoconductive drum is key issue to improve sharpness of an image and stability of reproducibility. In color image forming particularly, adjustment of the position by individual process unit is needed first. Further the degree of parallelization between each process unit is important to prevent occurrence of color skew of the image. As Patent Document 1 disclose, it has been popular that the degree of parallelization in respect to the photoconductive drum is maintained, for example, by adjusting the position of the LED print head serving as an exposing device via a frame portion which is coaxially connected to a rotation center of the photoconductive drum, in other words based on the frame portion. However, even by the above adjusting method, there is a case where the process unit is slightly deformed when the photoconductive drum and its drive mechanism, a developing roller, and a screw and its drive mechanism are assembled and connected. Thus the position LED print head is misaligned and the degree of parallelization is deteriorated. Further when the process unit is deformed with time, the accuracy of parallelization is further deteriorated.
Once the degree of parallelization in respect to the photoconductive drum is deteriorated, the process unit had to be dismantled from the image forming apparatus main boy so that the each member is reassembled and adjusted. Also, it was inconvenient that when the LED print head is replaced, the apparatus had to be carried into a maintenance room to carry out adjusting work, thus field service was extremely difficult.
Also, in order to prevent such phenomenon, described in the Patent Document 2, ensuring of the degree of parallelization in respect to the photoconductive drum is attempted to maintain, for example, by pressing a partial cylindrical section of a position setting section where a LED print head setting section and a developing device setting section are integrated, onto a cylindrical section of the photoconductive drum having the same diameter. However, since the position setting section and the photoconductive drum abut each other in sliding manner, it is not preferable as a positioning means and the degree of parallelization cannot be maintained stably.    Patent Document 1: Tokkai 2005-55781    Patent Document 2: Tokkai 2005-242119